The Action of Urginea Biirhei (Baker). 
201 
the frog's heart. Fig. 2 shows the effect of perfusing the cat's heart with 
1 in 200 tincture of Urginea Burkei. The upstroke denotes systole. a is 
the normal heart-beat, b to J show the effect on the heart when the 
experimental solution has perfused for 1, 2, o, 5, 7, 9, 10, 11 and 12 minutes 
respectively. This is the most characteristic action of slang-kop on the 
mammalian heart. 
(2) Heart-block may appear. This may be sinu-auriclar, the heart 
suddenly beating at half its previous rate, but is more commonly auriculo- 
ventricular, the ventricle l)eating at a slower rate than the auricle. Very 
soon the block becomes complete, no impulse passing from auricle to 
ventricle. In these cases it is noticealile that the tone of the ventricle 
increases as the drug is perfused, even after pulsations have ceased, and it 
soon is firmly contracted. 
(o) The heart after the ])reliiiiinary blowing may become (juick and 
irregular. Pulsus alternans and extra-systoles appear. These rarely pass 
off, but if they do the heart may finish as in (1) or (2). More comhionlv 
however, the extra-systoles are the precursors of lil)rillation of the auricles 
and ventricles, and the heart ceases after a short period of extreme 
irregularity. 
The rat's heart is less susceptible to the action of the i)oison than the 
cat's or ral!bit"s heart. 
(d) Action on the Mammalian Heart in situ. 
Method. — The animal — rabbit or cat — was anaesthetised with paraldehyde 
or urethane followed l)y ether. Cannulae were inserted into the trachea, left 
carotid artery and right jugular vein. Artificial respiration was commenced 
and the thorax opened in the middle line. A cardiometer, connected by 
rubber tubing to a recording tambour, was placed round the heart and the 
